1. Field of the Invention
The embodiments of the invention generally relate to a method and apparatus for dechucking a substrate.
2. Description of the Related Art
Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors. Generally, flat panels comprise two plates having a layer of liquid crystal material sandwiched therebetween. At least one of the plates includes at least one conductive film disposed thereon that is coupled to a power source. Power, supplied to the conductive film from the power supply, changes the orientation of the crystal material, creating a patterned display.
In order to manufacture these displays, a substrate, such as a glass or polymer workpiece, is typically subjected to a plurality of sequential processes to create devices, conductors and insulators on the substrate. Each of these processes is generally performed in a process chamber configured to perform a single step of the production process. In order to efficiently complete the entire sequence of processing steps, a number of process chambers are typically coupled to a central transfer chamber that houses a robot to facilitate transfer of the substrate between the process chambers. A processing platform having this configuration is generally known as a cluster tool, examples of which are the families of AKT plasma enhanced chemical vapor deposing (PECVD) processing platforms available from AKT America, Inc., of Santa Clara, Calif.
During operation, the robot disposed in the transfer chamber moves substrates between the chambers on an end effector. The robot positions the substrate over a substrate support disposed in the process chamber. The substrate support includes a transfer mechanism, such as a plurality of lift pins, that facilitates exchange of the substrate between the end effector and the substrate support.
As demand for flat panels has increased, so has the demand for larger sized substrates. For example, large area substrates utilized for flat panel fabrication have increased in area from 550 mm by 650 mm to over 1,500 mm by 1,800 mm in just a few years and are envisioned to exceed four square meters in the near future. This growth in the size of the large area substrates has presented new challenges in handling and production. For example, the larger contact surfaces between the substrate support and the substrate has increased the amount of static attraction of the substrate to substrate support after processing. This increased attraction between the substrate and substrate support requires more force to separate the substrate from the substrate support. The increased force exerted by the lift pins on the substrate, counteracted by the high attraction between the substrate and substrate support, results in an increased potential for substrate damage while being lifted (e.g., separated) from the substrate support. Moreover, in instances where the attraction between the substrate support and substrate is high, the center of the substrate may remain in contact with the substrate support as the lift pins begin to separate the substrate from the substrate support, thereby excessively deflecting the substrate. As the substrate deflects, the lift pins may slide along the bottom surface of the substrate, creating a scratch which may cause substrate breakage. Additionally, if the substrate “springs” back to its natural shape as the center of the substrate comes free of the substrate support, the substrate may jump and/or walk on the lift pins, potentially creating particles or substrate damage. Furthermore, if the substrate moves laterally relative to the lift pins, the substrate may become misaligned on the robot's end effector, thereby increasing the probability of substrate damage or poor processing results in subsequent processes due to substrate misalignment.
Therefore, there is a need for an improved method and apparatus for dechucking a substrate.